An Inca city on the saddle between two peaks at eight thousand feet, built around 1450 and abandoned perhaps a century later — probably to smallpox, which arrived ahead of the Spaniards themselves. The conquistadors never reached it and never learned it was there. The stones are fitted without mortar so closely that a knife blade will not go between them, and the Intihuatana, a carved pillar, casts almost no shadow at the solstices.